The present invention relates to a method for deburring sheet metal parts, such as can covers. More specifically, the invention relates to a method for producing can covers of sheet metal, particularly iron or steel sheet metal for containers especially cans for canning purposes. The blanks for such sheet metal parts, especially can covers, are stamped from sheet metal in the form of panels or continuous coils of sheet metal. Especially in connection with can covers provided with so-called rib tops the covers are stamped to have one or several openings therein for emptying the can and to provide a venting for facilitating the content removal. These openings in the can cover are surrounded by burrs along their edges due to the stamping operation. It is also known to provide the can covers after the stamping operation with protective coatings which are supposed to satisfactorily cover the burrs.
Thereafter, the holes in the cover are provided with a hermetic seal in the form of a flexible rib strip which is secured to the top of the cover either by an adhesive or by a so-called hot seal.
Covers of the type described above are known in the art, for example, from U.S. Pat. No. 3,292,828 or German Patent Publication (DE-AS) No. 2,519,709. Additionally, the present invention is applicable generally to all types of sheet metal parts having burrs including covers with only one hole either for the purpose of removing the can content and/or for venting the can.
The production by stamping, inevitably results in the formation of a burred edge around the stamped hole or holes and such burred edges have been the cause of problems such as injuries to the user, difficulties in providing a proper seal, corrosion problems which start along the burrs and may result in the spoiling of the can content, and so forth.
Attempts to avoid the just mentioned problems included providing the can cover on the side carrying the burrs with a respectively thick lacquer layer in which the stamping burr is embedded. However, a complete, continuously effective embedding of the burr is difficult and expensive because it requires continuous monitoring of the coating operation and the coating method is accordingly rather expensive. The burrs generally have an uneven configuration and therefore the complete coating of the burrs is difficult. Thus, corrosions may start in spots where parts of the burrs protrude from the coating. Also, in connection with can covers made of steel or iron sheet material a proper protective coating by tin plating or chromium plating could not be established satisfactorily heretofore, especially if one aims at providing a reliable and yet inexpensive coating operation for preventing the corrosion problems in the area of the stamping burrs. Similar problems may occur in connection with other types of sheet metals such as aluminum sheet metal or the like.